If the tooth is cracked after root canal treatment, it should be divided into these cases: 1.If the tooth is cracked, only the crown part does not reach the gum, this situation is not affected and can be directly piled for crown; 2.If the tooth is cracked and reaches below the gum located above the alveolar bone, it can be piled for crown after restoring the normal biological width through gingivectomy; 3.If the tooth is cracked up to 3mm below the alveolar bone, it can be piled for crown after restoring the biological width through crown lengthening; 4.If the tooth is cracked to the root more than 3mm below the alveolar bone, this tooth needs to be extracted.